1.College of Resources and Environment, Shandong Agricultural University;2.College of Land Resources and Surveying Engineering, Shandong Agriculture and Engineering University;3.Institute of Applied Ecology, Chinese Academy of Sciences;4.National Field Observation and Research Station of Shenyang Agroecosystems

Abstract:

【Objective】Soil salinization is one of the most severe agro-ecological problems that brings about widespread influences on ecosystem security and sustainable development of the agriculture, especially in the Yellow River Delta. It has been demonstrated that soil salinization has significant influences, too, on activity and structure of the soil microbial community through changing soil physicochemical properties. Yet, little has been documented about responses of microbial residues to soil salinization and relative contributions of microbial residues different in kind to soil organic matter (SOM) accumulation. As important constituents of microbial cell walls, amino sugars are considered to be a storage pool for immobilized C and N. Additionally, amino sugars are reliable microbial residue biomarkers thanks to their different origins. Muramic acid (MurA), glucosamine (GluN) and galactosamine (GalN) are amino sugars of particular importance, so far identified. MurA originates uniquely from bacteria as a component of peptidoglycan of bacterial cell walls, while GluN is mainly derived from fungal chitin, although bacterial cell walls and exoskeletons of soil invertebrates also make some contribution. GalN constitutes a significant fraction of the total amino sugar pool, but its origin in soil is still under debate. Therefore, amino sugars as unique and powerful microbial residue biomarkers can be used to indicate time-integrated microbial immobilization of extraneous C and N and stabilization of SOM on a relatively long-term scale, which is termed as “memory effect”.【Method】 Here, investigations were made of accumulation characteristics of the three types of amino sugars in the topsoil layers (0~20cm) of two crop fields of salinized soils, different in salinization level, i.e. light-salinized soil (LS) and moderate-salinized soil (MS), in the Yellow River Delta. In addition, relative contributions of fungal and bacterial residues to SOM accumulation and stabilization were explored by calculating ratio of GluN to MurA.【Result】Results show that soil salinization had significant influences on accumulations of total amino sugars and each. Total amino sugar was significantly higher in LS than in MS, but amino sugars of different kinds responded differently in content to salinization because of their specific origin. GluN content was much higher in LS than in MS. Although it is still not clear as to origin of GalN, it was similar to GluN in accumulation characteristics. Coming solely from bacteria, MurA was much higher in MS than in LS. Besides the much lower ratio of GluN to MurA in MS than in LS suggests that the relative contribution of bacterial residue to SOM accumulation was much higher in MS than in LS, and that the dominance of microbial groups shifted from fungi group to bacteria group with increasing soil salinity.【Conclusion】 As a whole, accumulation of fungal and bacterial residues is closely related to soil salinity, thus playing an important role in regulating stabilization and turnover of SOM in salinized soils. All the findings in this study have enriched our knowledge about microbial processes and related mechanisms of SOM transformation in salinized soils.